MATERIALS HIENGE& ENGIEERING ELSEVIER Materials Science and Engineering A 460-461(2007)306-313 www.elseviercom/locate/msea Effect of fiber architectures on thermal cycling damage of C/SiC composites in oxidizing atmosphere Hui Mei, aifei Cheng, Litong Zhang, Yongdong xu onal Key Laboratory of Thermostructure Composite Materials, Northwestem Polytechnical University. Xi'an Shaanxi 710072, People's Republic of China Received 22 November 2006: received in revised form 14 January 2007; accepted 27 February 2007 Abstract Mechanical response of two and three-dimensional carbon-fiber-reinforced Sic-matrix composites(2D and 3D C/SiCs) subjected simultaneously to thermal cycling and mechanical fatigue in oxidizing atmosphere was compared. Damage was assessed by residual strengths and microstructural characterization. Compared with 2D architecture, the braided 3D composites were shown to possess larger strain increment and strain rate during testing, higher retained strength after 50 thermal cycles, and better damage resistance against oxidation and thermal shock. Differences in oxidation regimes and in thermal shock resistance were ascribed in large part to differences in the fiber architectures. It is actually observed that the fiber architectures have critical influences on the orientations of coating cracking the constraints between neighboring fiber bundles, and the matrix crack propagating resistance, which can result eventually in the different damage resistance of the composites @2007 Elsevier B v. All rights rese Keywords: Ceramic matrix composites; Fiber architectures; Damage; Mechanical properties; Microstructure; Thermal cycling 1. Introduction icant mechanical stress in oxidizing atmosphere has not been reported yet, and under the environments mentioned above no Carbon-fiber-reinforced SiC-matrix composites(C/SiCs)are description involving damage comparison of the two compos- currently considered for applications as structural materials in ites with different fiber architectures can be found in the recent both aerospace and other industries [1-3. There are two main literature kinds of C/SiC composites: 2D C/SiC is usually used to fabricate The paper here provides experimental results on the response components such as plates, tubes and shells, and braided 3D of 2D and braided 3D C/SiC composites to thermal cycling C/SiC is used to fabricate items such as nozzles, combustor liners under mechanical fatigue in wet oxygen atmosphere. Residual and thrusters[4, 5]. In many of the instances, a part made of the properties and microstructures of the thermally cycled compos- composite materials is likely to undergo simultaneously thermal ite specimens are presented, and damage induced in the two cycling and mechanical fatigue in severe service environments. architecture composites is evaluated and compared. Efforts were Many previous efforts have been devoted to investigation on made in this investigation to correlate different preform struc- thermal shock/cycling behav the C/SiC composites with tures (i.e, fiber architectures) with damage resistance of the the same preform structures(either 2D or 3D)in absence of the composites against the oxidation and thermal shock external mechanical stress [6-10]. Recently, thermal properties of 2D and 3D C/SiC composites have been basically reported 2. Experimental from room temperature to 1400C by Cheng et al. [11], and the static mechanical responses of 2D and 3D C/C composites 2. Materials preparation were compared by Aly-Hassan et al. [12]. However, mechanical response of the C/SiC composites to thermal cycles and signif- Three-dimensional(braided 3D) preforms were braided by a four-step method using lk T-300 carbon fibers(braiding angle N 220), and two-dimensional(2D)preforms were lami- Corresponding author. Tel: +86 29 88494616: fax: +86 29 88494620 nated with the same lK T-300 carbon fiber fabrics(10/90D) E-mailaddress:phdhuimei@yahoo.com(H.Mei) The composites were prepared by isothermal CVI technolog 0921-5093/S-see front matter O 2007 Elsevier B v. All rights reserved doi:10.1016/msea.2007.02.104Materials Science and Engineering A 460–461 (2007) 306–313 Effect of fiber architectures on thermal cycling damage of C/SiC composites in oxidizing atmosphere Hui Mei ∗, Laifei Cheng, Litong Zhang, Yongdong Xu National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi’an Shaanxi 710072, People’s Republic of China Received 22 November 2006; received in revised form 14 January 2007; accepted 27 February 2007 Abstract Mechanical response of two and three-dimensional carbon-fiber-reinforced SiC-matrix composites (2D and 3D C/SiCs) subjected simultaneously to thermal cycling and mechanical fatigue in oxidizing atmosphere was compared. Damage was assessed by residual strengths and microstructural characterization. Compared with 2D architecture, the braided 3D composites were shown to possess larger strain increment and strain rate during testing, higher retained strength after 50 thermal cycles, and better damage resistance against oxidation and thermal shock. Differences in oxidation regimes and in thermal shock resistance were ascribed in large part to differences in the fiber architectures. It is actually observed that the fiber architectures have critical influences on the orientations of coating cracking, the constraints between neighboring fiber bundles, and the matrix crack propagating resistance, which can result eventually in the different damage resistance of the composites. © 2007 Elsevier B.V. All rights reserved. Keywords: Ceramic matrix composites; Fiber architectures; Damage; Mechanical properties; Microstructure; Thermal cycling 1. Introduction Carbon-fiber-reinforced SiC-matrix composites (C/SiCs) are currently considered for applications as structural materials in both aerospace and other industries [1–3]. There are two main kinds of C/SiC composites: 2D C/SiC is usually used to fabricate components such as plates, tubes and shells, and braided 3D C/SiC is used to fabricate items such as nozzles, combustor liners and thrusters [4,5]. In many of the instances, a part made of the composite materials is likely to undergo simultaneously thermal cycling and mechanical fatigue in severe service environments. Many previous efforts have been devoted to investigation on thermal shock/cycling behavior of the C/SiC composites with the same preform structures (either 2D or 3D) in absence of the external mechanical stress [6–10]. Recently, thermal properties of 2D and 3D C/SiC composites have been basically reported from room temperature to 1400 ◦C by Cheng et al. [11], and the static mechanical responses of 2D and 3D C/C composites were compared by Aly-Hassan et al. [12]. However, mechanical response of the C/SiC composites to thermal cycles and signif- ∗ Corresponding author. Tel.: +86 29 88494616; fax: +86 29 88494620. E-mail address: phdhuimei@yahoo.com (H. Mei). icant mechanical stress in oxidizing atmosphere has not been reported yet, and under the environments mentioned above no description involving damage comparison of the two compos￾ites with different fiber architectures can be found in the recent literature. The paper here provides experimental results on the response of 2D and braided 3D C/SiC composites to thermal cycling under mechanical fatigue in wet oxygen atmosphere. Residual properties and microstructures of the thermally cycled compos￾ite specimens are presented, and damage induced in the two architecture composites is evaluated and compared. Efforts were made in this investigation to correlate different preform struc￾tures (i.e., fiber architectures) with damage resistance of the composites against the oxidation and thermal shock. 2. Experimental 2.1. Materials preparation Three-dimensional (braided 3D) preforms were braided by a four-step method using 1K T-300 carbon fibers (braiding angle ≈ 22◦), and two-dimensional (2D) preforms were lami￾nated with the same 1K T-300 carbon fiber fabrics ([0◦/90◦]). The composites were prepared by isothermal CVI technology 0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.02.104